John g-ast



STATES PATENT Enron.

JOHN GAST, OF BROOKLYN, NEW YORK.

VULCANIZED-RUBBER PAD FOR STIGMOGRAPHS.

SPECIFICATION forming part of Letters Patent No. 242,627, dated June 7,1881.

Application filed March 25, 1881. (No model.)

To all whom it may concern:

Be it known that I, JOHN GAST, of Brooklyn, in the county of Kings andState of New York, have invented a new and useful Improvement inVulcanized-Rubber Pads for Stigmographs,of which the following is aspecification.

The invention relates to an improved pad for stippling 011 lithographicstones, zinc or metal f plates, and for other uses in the art oflithography.

The object of the invention is to produce a pad whereby stipple'w'orkmay be rapidly and artistically accomplished, and which will be of suchelasticity that it will yield sufficiently to pressure, and which willbe of the necessary durability, and neither shrink, break, nor crackwhen subjected to ordinary atmospheric changes. I have termed the padmentioned a stigmograph, by which it will be described hereinafter.

The following is a formula of the ingredients constituting the preferredcomposition out of which the stigmograph is made: Ten (10) pounds ofrubber; twelve (12) ounces of sulphur; forty-eight (48) ounces ofvermillion; twenty (20) ounces of French zinc-white; four (4;) ounces ofpowdered soapstone. These ingredients are thoroughly mixed together,gentle heat being applied to render the mass homogeneous.

While a compound consisting of the abovenamed ingredients is preferredfor the formation of the stigmograph, it is plain that they may bevaried somewhat without departing from the essence of the invention. Forinstance, in lieu of employing vermillion, which gives the compound areddish color, I may use an analogous material. If a yellow color is tobe produced, I employ chromeyellow and cadmium; if a green color, I usechrome-yellow or lemon-yellow and Antwerp blue, Prussian, Milori, or anyother blue. For a blue color I prefer to use chrome-green andultramarine or cobalt. It will be desirable, however, to employ a colorof about the same relative weight and bulk as vcrmillion to attain theproper degree of elasticity. It the color used is much lighter in weightthan vermillion, its proportion of weight should be made up with thezinc-white or its equivalent. The compound is now in one homogeneousmass, and my object is to reduce it to small pieces or pads of propersize and thickness, one side of the same being smooth and the other sidehaving a stippled or grained surface in relief, the piece or pad beingalso vulcanized.

The process of treating the compound to form the pads described will beas follows: I first draw or stipple on stone with pen the style and sizeof grain of stipple-work to be produced in relief on the surface of thepad or stigmograph. Of course the size and style of grain may be variedat will. From the stone aprint of the stipple-work is taken on whitepaper, from which relief-plates are made by the photo-en gravin gprocess or any other suitable method. 1 next take plaster casts ornegative metal casts from the relief-plates, and from these plaster ormetal casts the rubber pads or stigmographs receive the impression ofthe stipple-work. The pads, having been thus formed, are then vulcanizedaccording to the following method: The rubber compound is rolled into athin sheet of, say, about oneeighth of an inch in thickness, and thencut into smaller pieces or pads of proper size to fit the plasternegatives, (or plaster molds,) upon which they are placed and pressedfirmly down by a smooth polished metallic plate applied to the back ofthe rubber, whereby the said back is given a smooth surface.

As a precaution, prior to placing the metal plate upon the rubber Iprefer to first powder the back of the pad with fine soapstone-dust andthen spread a smooth sheet of tin-foil over it, afterward placing thepolished metal plate upon the tin-foil. This is done to prevent themetal from blackening the back of the pad during the vulcanization ofthe latter. The metal plate is screwed tightly to the plaster moldbymea-ns of a pair of clam p-irons of usual construction. In order toprevent the plaster mold from breaking during the operation, it may beformed within an iron chase of proper size. The plaster mold, with therubber held upon its surface by the polished plate and clamp-irons, isthen introduced into a steamvulcapizer and submitted to a heat of about265 Fahrenheit for a space of about four and one-half to five hours. .Irecommend that great care be exercised in this step of the process,since the proper vulcanization adds greatlyin giving the pad therequired toughness and elasticity, so as to be just suitable andapplicable to transfer an impression by the touch of the finger, hand,or stylus. After the vulcanization the pads are taken outand are readyfor use, one side being smooth and the other bearing the impression ofstipple-work taken from the plaster mold.

The foregoing is an accurate description of the stigmograph and the modeof its manufacture. In using it for stippling stone the following stepsshould be observed: The outlines of the design being drawn, the solidsfilled in, and the sharp lines gummed out in the usual way, thestigmograph, which has received a coating of lithographic transfer-inkfrom a common priutcrs roller or otherwise, is laid over the stone wherewanted. If an even tint is desired, the instrument is pressed gently andevenly with the hand or otherwise; and if a darker tint or thicker dotsare required, the pressure is increased.

If it is not desired to gum out the lights on the stone, they may bescraped out, like those on what are known as rub tints or asphaltdrawings, and beautiful soft effects produced.

The stigmograph described, in lieu of being a flat printing-pad, may bemounted upon a roller or otherwise, as may be preferred.

I am aware that elastic printingfil m s, handstamps, 850., have beenlong known in the arts; but none of them, as far as I am informed, havepossessed that peculiar degree of elasticity upon which I rely, which isessential to the production of really artistic effects, and thepermanent preservation of which is necessary in an instrument ofpractical value.

What I claim as new is- 1. A stigmograph composed of rubber, sulphur, acolor, French zinc-white, and powdered soapstone, in about theproportions stated.

2. A stigmograph formed from a sheet con sistin g of rubber, sulphur, acolor, French zincwhite, and powdered soapstone, and vulcanized.

3. A stigmograph consisting ofa sheet formed from a rubber compound andvulcanized bybeing subjected to a heat of about 265 Fahrenheit for aspace of from about four and onehalf to five hours, substantially as setforth.

In testimony that I claim the foregoing improvement in vulcanized-rubberpads, as above described, I have hereunto set my hand this 24th day ofMarch, 1881.

JOHN GAST.

Witnesses:

J OHN T. FINN, HARRY O. DOYLE.

